In an election between two candidates, the defeated candidate secured 42% of the valid votes polled and lost the election by 7,68,400 votes. If 82,560 votes were declared invalid and 20% people did NOT cast their vote, then the invalid votes were what percentage (rounded off to 1 decimal place) of the votes which people did NOT cast?

Answer: Option D

Total number of votes = 5x
Votes polled = 4x
Valid votes = 4x - 82560
Invalid votes = 82560
Defeated candidate = 42% of valid votes
Winning n = 58% of valid votes
16% of valid votes (difference) = 768400
16%(4x - 82560) = 768400
4x = 4802500 + 82560
x = 1221265
$$\begin{array}{rl}& \text{Required}\%=\frac{\text{Invalid votes}}{\text{Number of people not voted}}\times 100\\ & =\frac{82560}{1221265}\times 100\\ & =6.76\%\cong 6.8\%\end{array}$$